1. Field of the Invention
This invention relates to light distribution control of a head lamp device for changing a lighting region in rightward and leftward directions.
2. Description of Relevant Art
Hitherto, various head lamp devices capable of changing a lighting region in rightward and leftward directions have been proposed. In almost all of them, basically the lighting region is controlled to change in response to a steering angle of the steering wheel (Japanese laid-open patent publications No. Sho 62-77249, No. Hei 3-14742 etc.) and the lighting region of the head lamp is changed to a direction of the steering to increase a lighting amount in the direction to which the vehicle is just going to advance.
Accordingly, a vehicle having such a head lamp device is specially provided with a steering angle sensor for detecting the steering angle of the steering wheel. When using the steering angle sensor, means for detecting a basis point of the steering angle is necessary in addition in order to obtain a steering angle with respect to the vehicle body.
Conventionally, a vehicle has various sensors mounted thereon, and in a vehicle installed with an anti-lock braking system (ABS), a traction control system (TCS) or the like, sensors for detecting rotational speeds of wheels are provided. Particularly, ABS tends to be installed widely in many kinds of vehicles now and in the future.
It is uneconomical that in spite of above-mentioned various sensors conventionally provided on vehicles, that the steering angle sensor and the steering angle basis point detecting means are added for changing the lighting region of a head lamp device. Thus, if a sensor used for other object can be utilized for changing the lighting region, the cost will be reduced.